1. Field of the Invention
The present invention relates to a radio-frequency (RF) device and wireless communication device, and more particularly, to an RF device and wireless communication device capable of maintaining radiating efficiency as well as reducing dimensions and increasing a sensing distance of the RF device.
2. Description of the Prior Art
A wireless communication device is equipped with an antenna to emit or receive radio waves, so as to exchange radio-frequency (RF) signals and access a wireless communication system. Since radio waves are high-frequency sinusoidal signals, every country in the world standardizes the power of radio waves mainly for preventing from affecting users and/or interfering operations of other wireless communication devices. For example, the International Commission on Non-Ionizing Radiation Protection (ICNIRP) recommends that the value of Specific Absorption Rate (SAR) shall not exceed 2.0 W/Kg, while the Federal Communications Commission (FCC) recommends that the value of SAR shall not exceed 1.6 W/Kg. SAR is a measure of the amount of radio frequency energy absorbed by the living body in a normal electromagnetic radiation environment, and watts per kilogram (W/Kg) is the unit of SAR. Besides, since different communication products are used under different conditions, a distance factor is further taken into consideration when measuring the value of SAR. For example, according to the general regulation, measurement of SAR for a handset wireless communication device such as a mobile device or a smart phone should be taken under a condition that the distance between the handset wireless communication device and a human body is 20 cm.
As well known to those skilled in the art, antenna efficiency is usually affected if attempting to reduce interferences of the wireless communication device itself to the outside environment (i.e. to reduce SAR value of the wireless communication device). Therefore, many methods have been disclosed in the prior art in order to maintain the antenna efficiency. One method is by using a proximity sensor to detect the approach of a human body. That is, the RF power of the wireless communication device is reduced when the proximity sensor detects that a human body is approaching, whereas the RF power of the wireless communication device is kept or moderately increased when the proximity sensor does not detect the approach of any human body. In such a condition, interference can be reduced, and meanwhile, antenna efficiency is kept. In the prior art, the proximity sensor includes a receiver or sensor which contains metal materials to detect capacitance variation, so as to determine whether a human body is approaching. However, the included receiver or sensor affects the antenna efficiency, and therefore, additional cost is required to adjust the antenna. Thus, it is a common goal in the industry to design an antenna which complies with the regulations for the SAR value and maintains the antenna efficiency as well.